Comparative thermodynamic assessment of pyroprocessing and chlorination for the treatment of LWR spent nuclear fuel

The disposal burden of spent nuclear fuel (SNF) can be reduced by processing it to separate and collect constituent nuclides based on their characteristics. This study evaluates and compares the treatment efficiencies of pyroprocessing and chlorination, based on thermodynamic equilibrium calculations, using light water reactor (LWR) SNF, from which volatile fission products have been removed through high-temperature heat treatment, as the reference material. Pyroprocessing, consisting of oxide reduction (OR), electrorefining (ER), and electrowinning (EW), was effective not only in separating high-decay-heat, short-lived fission products (FPs) from LWR SNF but also in group recovery of transuranic elements (TRUs) that can be recycled as nuclear fuel. The chlorination process, which involves chlorination with NH₄Cl, followed by precipitation with Li₂CO₃ in LiCl-KCl molten salt, was effective in separating high-decay-heat, short-lived FPs from LWR SNF. A hybrid process integrating the EW step of pyroprocessing and the NH₄Cl chlorination step of the chlorination process was proposed in this study. Thermodynamic analysis indicates its effectiveness in high-decay-heat, short-lived FPs separation and group recovery of TRUs, demonstrating its potential as a viable option to reduce the disposal burden of high-level waste.